The site was created last November as part of FBI attempts to clean up damage created by a cyber-crime ring that was busted in Estonia. When you visit, the site does a quick analysis of your machine and advises whether it's infected with this particular problem. (You should also, of course, always maintain safeguards against viruses in general.)

The virus, called "DNSChanger," allegedly infected as many as 4 million computers (both Macs and PCs) worldwide, including an estimated 570,000 in the United States, and netted at least $14 million.

DNS stands for Domain Name System. It's the Internet's way of translating a human-readable "domain name" such as www.aarp.org into a numbers-only "IP address" that computers can understand.

Here's how the virus worms its way into your computer: Normally, when you type in a name to access a site, you link to a DNS server that lists that site's IP address. If you've been hit by DNSChanger, instead of this happening, you will be directed to rogue DNS servers controlled by cyber thieves.

The end effect is that when you type in the name of a well-known website, you are instead taken to a scam site that looks just like the site you are trying to access. The crooks made their millions by tricking unsuspecting users into making bogus online purchases and by collecting commissions when visitors clicked on advertisements.

"When users of infected computers clicked on the link for the official website of iTunes, for example, they were instead taken to a website for a business unaffiliated with Apple Inc.," the FBI says. "There was a level of complexity here that we haven't seen before."

If you connect to the dcwg.org website, you'll be informed whether your computer is infected with DNSChanger.

If the news is good, you'll see a green logo with the message: "DNS Resolution = Green. Your computer appears to be looking up IP addresses correctly!" Those words mean you don't need to do anything.

But if you get a message with a red logo indicating your computer is infected, you'll be directed to a new page and websites that provide antivirus software that can remove the DNSChanger virus.

So check by July 9, or your Internet surfing may be beached.

Sid Kirchheimer is the author of Scam-Proof Your Life, published by AARP Books/Sterling.